The present invention relates to elevator systems. More particularly the invention relates to a termination for a flexible flat tension member.
A conventional traction elevator system includes a car, a counterweight, two or more ropes (tension members) interconnecting the car and counterweights; terminations for each end of the ropes at the connection points with the car and counterweights, a traction sheave to move the ropes and a machine to rotate the traction sheave. The ropes have traditionally been formed of laid or twisted steel wire which are easily and reliably terminated by means such as compression terminations and potted terminations.
Compression type terminations for steel ropes of larger diameters (conventional steel elevator ropes) are extremely effective and reliable. The range of pressures placed on such terminations is reasonably broad without adverse consequence. Providing that the pressure applied is somewhere reasonably above the threshold pressure for retaining the ropes, the termination is effective.
With an industry trend toward flat ropes, those ropes having small cross-section cords and polymeric jackets, significantly more criticality is involved in effectively terminating the same. More specifically, the polymeric coating can creep to even 50% of its original thickness when subjected to pressure. Prior art knowledge which teaches one to exceed a threshold omits a critical parameter for a flexible flat tension member. Upper limits on compression are also important for such tension members.
Since current knowledge in the art of tension member terminations is less than sublime for flexible flat tension members due both to the small cord diameter and the jacket properties discussed above, the art is in need of a tension member terminating device which specifically optimizes terminations of the flexible flat tension members currently emerging in the field.
A flexible flat rope (tension member) termination device is disclosed herein which comprises a socket, the socket including a pair of pins, a load side bearing wall having a friction surface, and a cut side bearing wall having a friction surface. The socket defines an interior hollow sized to accept two wedges in an opposed position relative to one another which together provide compressive and frictional forces that are desirable for securing a flat rope therein, the flat rope is threaded from a load end of the termination device around a first wedge, then back downwardly around a second wedge and then upwardly to its end. The arrangement provides about 35 MPa of compressive force on the flat rope over an effective friction surface of about 75 square centimeters. No fasteners are necessary during site assembly thus speeding assembly time and reducing cost considerations while optimizing termination reliability. In order to increase the coefficient of friction of the device, the surfaces upon which the flat rope will make contact are preferably textured. By increasing friction through textured surfaces the compressive force necessary to secure the flat rope is lower. This is desirable to reduce creep and thus extend the useful service life of the flat rope.
In addition to the foregoing, the reduction in creep allows for monitoring of the condition of the flat rope using magnetic flux leakage or electrical conductivity. Since creep is effectively eliminated, grounding of the rope does not occur. Thus magnetic or electrical conductivity may be monitored from one end of the rope to the other end of the rope. Since losses due to grounding are eliminated in the above discussed termination, conductive readings of the strands of the rope will accurately reflect the condition of the strands.
In another embodiment of the invention, a pair of capstans are employed to provide the necessary frictionally compressional forces required to terminate a flexible flat rope. One capstan is fixed while a second capstan is moveable toward or away from the first capstan. The device may be used to terminate a tension member whose working end extends downwardly from the device or whose working end extends upwardly from the device.